Recombinant Cronobacter sakazakii UPF0208 membrane protein ESA_00924 (ESA_00924)

What are the confirmed structural domains in ESA_00924?

While the complete three-dimensional structure of ESA_00924 has not been fully characterized through crystallography or NMR studies, bioinformatic analysis suggests this protein belongs to the UPF0208 family of membrane proteins. The protein contains predicted alpha-helical transmembrane domains typical of integral membrane proteins . Sequence analysis indicates potential structural homology with other bacterial membrane proteins involved in small molecule transport or signaling. Advanced structure prediction tools suggest the presence of at least one significant transmembrane domain between residues 60-80, though experimental confirmation through techniques like circular dichroism spectroscopy or controlled proteolysis would be required to validate these predictions.

Is ESA_00924 protein conserved across different Cronobacter species?

Sequence conservation analysis indicates that ESA_00924 shows high conservation among Cronobacter sakazakii strains, including those isolated from clinical and food sources. This conservation suggests potential functional importance in bacterial physiology or pathogenesis . When addressing this question experimentally, researchers should perform comprehensive sequence alignment analysis across various Cronobacter species and strains. Additionally, examining conservation in related Enterobacteriaceae family members may provide evolutionary insights into the protein's function. The high degree of conservation observed in virulent strains particularly warrants investigation into whether this protein contributes to bacterial survival in stressful environments like reconstituted powdered infant formula.

What are the optimal conditions for expression and purification of recombinant ESA_00924?

For optimal expression of recombinant ESA_00924, the protein can be successfully expressed in E. coli expression systems with an N-terminal His-tag to facilitate purification . The recommended expression protocol includes:

• Transformation into an appropriate E. coli strain (BL21(DE3) is commonly used)

• Culture in rich media (such as LB or 2YT) supplemented with appropriate antibiotic

• Induction with IPTG (0.5-1.0 mM) at mid-log phase (OD600 ~0.6-0.8)

• Post-induction growth at 25-30°C for 4-6 hours to minimize inclusion body formation

• Cell harvest by centrifugation (4500 rpm, 15 minutes)

For purification, researchers should consider:

• Cell lysis using sonication or pressure-based methods in buffer containing mild detergents (0.5-1% Triton X-100 or n-Dodecyl β-D-maltoside) to solubilize membrane proteins

• Affinity chromatography using Ni-NTA resin with imidazole gradient elution (20-250 mM)

• Size exclusion chromatography for further purification and buffer exchange

Membrane proteins like ESA_00924 can be challenging to work with, so maintaining protein solubility through the addition of appropriate detergents throughout the purification process is critical for successful isolation of functional protein.

How should researchers assess the functional activity of purified ESA_00924?

• Membrane incorporation assays: Verify proper folding and membrane insertion using reconstituted liposomes or nanodiscs

• Binding assays: If suspected to interact with host factors, pull-down assays or surface plasmon resonance can detect binding partners

• Thermal shift assays: Evaluate protein stability under various conditions

• Circular dichroism: Confirm secondary structure formation consistent with predictions

For more advanced functional assessments, researchers could create knockout mutants (ΔESA_00924) in C. sakazakii and evaluate phenotypic changes in:

• Growth rates under various stress conditions

• Antibiotic susceptibility profiles

• Biofilm formation capacity

• Virulence in cell culture infection models

Cell culture models using HEp-2 cells provide a valuable system for investigating the role of ESA_00924 in bacterial adhesion and invasion, similar to methodologies employed for studying other C. sakazakii virulence factors .

What are the recommended storage conditions for maintaining ESA_00924 protein stability?

To maintain optimal stability of purified recombinant ESA_00924 protein, the following storage conditions are recommended:

• Short-term storage (up to one week): Store working aliquots at 4°C in Tris/PBS-based buffer at pH 8.0

• Long-term storage: Store at -20°C/-80°C with 6% trehalose as a cryoprotectant

• For extended preservation, add 5-50% glycerol (final concentration) and store at -80°C

Importantly, repeated freeze-thaw cycles significantly reduce protein stability and should be avoided. Therefore, dividing the purified protein into single-use aliquots before freezing is strongly recommended. Before use, researchers should briefly centrifuge thawed protein to collect any precipitated material and reconstitute in sterile deionized water to a concentration of 0.1-1.0 mg/mL for experimental applications . The addition of mild detergents may be necessary to maintain membrane protein solubility during storage and subsequent experimental procedures.

What is the potential role of ESA_00924 in Cronobacter sakazakii virulence?

While the specific role of ESA_00924 in C. sakazakii virulence has not been fully elucidated, several lines of evidence suggest potential involvement in pathogenesis:

• As a membrane protein, ESA_00924 may participate in host-pathogen interactions, potentially mediating adhesion to host cells or environmental persistence

• Its conservation across virulent strains suggests functional importance

• Membrane proteins often contribute to antibiotic resistance mechanisms, and C. sakazakii strains exhibit significant antibiotic resistance profiles (83% resistant to multiple antibiotics)

To experimentally investigate ESA_00924's role in virulence, researchers should consider:

• Creating isogenic knockout mutants and evaluating their invasion capacity in cell culture models

• Conducting comparative transcriptomics between wild-type and mutant strains under infection-relevant conditions

• Performing immunolocalization studies to determine if the protein is exposed on the bacterial surface

• Testing whether antibodies against ESA_00924 inhibit bacterial adhesion or invasion of host cells

Understanding ESA_00924's role in virulence could provide insights into C. sakazakii pathogenesis mechanisms that lead to severe infections with 40-80% lethality rates in neonatal infections .

Is there evidence for ESA_00924 involvement in biofilm formation?

Biofilm formation represents an important virulence mechanism for C. sakazakii, particularly in clinical settings and food preparation environments. While direct evidence linking ESA_00924 to biofilm formation is currently limited, its identity as a membrane protein makes it a candidate for involvement in this process. Researchers investigating this question should:

• Compare biofilm formation capacity between wild-type and ESA_00924 knockout strains using:

  • Crystal violet staining quantification

  • Confocal microscopy with fluorescently-labeled bacteria

  • Flow cell systems to evaluate biofilm development under dynamic conditions

• Analyze ESA_00924 expression levels in:

  • Planktonic versus biofilm-associated cells

  • Different stages of biofilm development

  • Biofilms formed on different surfaces (plastic, stainless steel, glass)

Biofilm formation enhances C. sakazakii survival in milk kitchen environments and feeding equipment, potentially contributing to outbreaks . If ESA_00924 participates in biofilm formation, it could represent a novel target for interventions aimed at reducing environmental persistence of this pathogen in hospital settings.

How might ESA_00924 interact with host immune defenses during infection?

This advanced research question addresses potential molecular interactions between ESA_00924 and host immune components. While current evidence on specific ESA_00924 interactions is limited, membrane proteins often engage with host immune factors. Researchers investigating this question should consider:

• Experimental approaches to detect interactions:

  • Co-immunoprecipitation with host immune components from infected cell lysates

  • Yeast two-hybrid or bacterial two-hybrid screening against human immune protein libraries

  • Surface plasmon resonance using purified ESA_00924 and candidate immune proteins

• Functional immunological assays:

  • Neutrophil activation and phagocytosis assays comparing wild-type and ΔESA_00924 strains

  • Cytokine induction profiles in human cell lines exposed to purified ESA_00924

  • Complement activation and resistance assays

Given that C. sakazakii causes severe neonatal infections with high mortality rates , understanding how its membrane proteins might modulate host immunity is crucial. The immature immune system of neonates may be particularly susceptible to immune evasion mechanisms mediated by bacterial membrane proteins like ESA_00924.

What structural features distinguish ESA_00924 from homologous proteins in non-pathogenic bacteria?

Comparative structural biology approaches can reveal unique features of ESA_00924 that may contribute to C. sakazakii pathogenicity. Researchers should employ a multi-faceted approach:

• Computational analysis:

  • Multiple sequence alignment with homologs from pathogenic and non-pathogenic species

  • Identification of pathogen-specific sequence motifs or domains

  • Molecular modeling to predict structural differences

• Experimental approaches:

  • Site-directed mutagenesis of predicted functionally important residues

  • Domain swapping experiments between pathogenic and non-pathogenic homologs

  • Structural studies (X-ray crystallography or cryo-EM) to resolve three-dimensional differences

• Functional validation:

  • Complementation assays in knockout strains using chimeric proteins

  • Virulence testing with strains expressing modified versions of ESA_00924

Identifying structural features unique to pathogenic versions of this protein could provide valuable insights for developing targeted antimicrobial strategies that specifically inhibit virulent Cronobacter strains without affecting commensal bacteria.

How does the antibiotic resistance profile correlate with ESA_00924 expression in clinical isolates?

Given that 83% of C. sakazakii strains exhibit resistance to multiple antibiotics , understanding the potential relationship between ESA_00924 and antibiotic resistance mechanisms represents an important research question. Researchers should design experiments to:

• Quantify ESA_00924 expression levels in:

  • Antibiotic-resistant versus susceptible clinical isolates

  • Strains before and after development of induced resistance

  • Strains exposed to sublethal antibiotic concentrations

• Determine if ESA_00924 overexpression affects:

  • Minimum inhibitory concentrations (MICs) for various antibiotics

  • Membrane permeability to antibiotic compounds

  • Expression of known antibiotic resistance genes

• Investigate protein-protein interactions between ESA_00924 and:

  • Known multidrug efflux pumps

  • Membrane proteins involved in antibiotic resistance

This research direction is particularly relevant for clinical management of C. sakazakii infections, which often occur in vulnerable neonatal populations. If ESA_00924 contributes to antibiotic resistance, targeting this protein could potentially enhance antibiotic efficacy against resistant strains.

What are the advantages and limitations of different heterologous expression systems for ESA_00924?

Selecting an appropriate expression system is critical for successful production of recombinant membrane proteins like ESA_00924. Researchers should consider:

What cell culture models are most appropriate for studying ESA_00924's role in host-pathogen interactions?

Selection of appropriate cell culture models is essential for investigating potential roles of ESA_00924 in Cronobacter sakazakii pathogenesis:

Research has established protocols for using HEp-2 cells to study C. sakazakii invasion, where bacteria are cultured overnight in 1% tryptone, and cells are infected using 10^8 cells/ml bacterial suspensions with 3-hour incubation periods . Quantification using colony-forming unit (CFU) determination provides reliable measurements of bacterial-host cell interactions. When investigating ESA_00924 specifically, comparing wild-type and knockout strains in these established models would provide valuable insights into the protein's role in pathogenesis.

What are the most promising research directions for understanding ESA_00924's role in C. sakazakii biology?

Based on current knowledge gaps, several high-priority research directions for ESA_00924 should be considered:

• Structural characterization:

  • Determine three-dimensional structure through X-ray crystallography or cryo-EM

  • Identify binding partners through pull-down assays and proteomics

  • Delineate membrane topology using accessibility labeling

• Functional studies:

  • Generate and characterize ΔESA_00924 knockout strains

  • Evaluate phenotypic changes in growth, stress resistance, and virulence

  • Perform complementation studies with site-directed mutants

• Infection biology:

  • Investigate ESA_00924's role in various stages of infection

  • Determine expression patterns during host cell interaction

  • Evaluate potential as vaccine target or diagnostic marker

The multifaceted approach to studying this membrane protein could provide significant insights into C. sakazakii pathogenesis mechanisms, potentially leading to novel intervention strategies to address infections with 40-80% lethality rates in neonatal populations . Understanding the molecular basis of virulence factors like ESA_00924 has direct implications for improving infant food safety and developing targeted antimicrobial treatments.

How might understanding ESA_00924 contribute to novel control strategies for C. sakazakii?

Knowledge of ESA_00924 structure and function could inform development of novel intervention strategies:

• Targeted antimicrobials:

  • Structure-based design of specific inhibitors

  • Peptides that disrupt membrane protein function

  • Identification of essential functional motifs

• Improved detection methods:

  • Development of antibodies against exposed epitopes

  • Design of specific nucleic acid probes for rapid detection

  • Creation of biosensors targeting this conserved protein

• Risk assessment applications:

  • Correlation between ESA_00924 variants and virulence potential

  • Development of markers for particularly harmful strains

  • Improved models for C. sakazakii growth and survival in formula

With C. sakazakii showing rapid growth in reconstituted PIF (generation time of 0.41h at 35°C) , developing targeted intervention strategies based on key virulence factors becomes increasingly important. If ESA_00924 proves essential for environmental persistence or infection, targeting this protein could provide novel approaches to control this significant neonatal pathogen and improve infant food safety.